//https://leetcode.cn/problems/peak-index-in-a-mountain-array/description/

class Solution {
public:
    int peakIndexInMountainArray(vector<int>& arr) {
        int left = 0, right = arr.size() - 1;
        while (left < right) {
            int mid = left + (right - left + 1) / 2;
            if (arr[mid] > arr[mid - 1])
                left = mid;
            else
                right = mid - 1;
        }
        return left;
    }
};